City plans to hit invasive plant with herbicide injections.

It’s a wily green invader so pervasive, so aggressive, and so entrenched that the city is enlisting a chemical weapon that some believe often does more harm than good.

But this WMD – a synthetic herbicide formerly banned from city use – will be deployed with the precision of a smart-bomb in stepped-up efforts to eradicate the invasive knotweed, according to full-time weed fighter Len Beil.

“Unfortunately, the only real way to control it is through herbicide,” he said, standing with weed cutters in hand near a veritable forest of knotweed at the south edge of Pritchard Park. “We’ll use (herbicide) as judiciously as we can because we have to do something.

“Knotweed, I’ve seen in the last couple years, has gotten bad – but it’s ready to become explosive.”

The City Council on Wednesday amended a ban on the use of numerous pesticides and herbicides by public works crews.

The amended rules allow glyphosate, a chemical considered toxic to humans and animals, for controlled use against knotweed on city property.

The herbicide will be injected into the individual knotweed stems. Spraying and other forms of treatment will still be prohibited.

A member of the buckwheat family and resembling bamboo, knotweed was imported from Asia as an ornamental plant to spice up home gardens.

But the plant wouldn’t stay put. It spread rapidly, often tunneling its roots up to 65 feet under roads to its preferred habitat: stream banks. There it can grow with such density that salmon and other wildlife are pushed out.

The Kitsap County Noxious Weed Control Board has marked knotweed as a high priority for preventative strategies that limit the plant’s spread to other parts of the state.

“There is no way to feasibly control knotweed using manual techniques given the extent of our infestation,” said Deborah Rudnick, an aquatic ecologist who advised the city on the controlled use of glyphosate. “It is simply not a viable option if our goal is effective eradication.”

Even other aggressive non-native plants lists are no match for knotweed. Beil pointed to a patch of Himalayan blackberry dominating an Eagle Harbor Drive hillside.

But at the thick bramble’s center was a contingent of knotweed Beil said has grown wider in recent months.

Roadside swaths are creeping into Pritchard Park, foreshadowing a day when knotweed blankets may cover its forest and shoreline, said Beil.

“This will take over Pritchard Park,” he said. “It will choke streams and grow all the way down to where the saltwater stops. What do we do then? Have somebody mow Pritchard Park every week?”

Four flavors

Four varieties of knotweed grow on Bainbridge Island, including giant, Japanese and Himalayan. Bohemian knotweed – a crossbreed of giant and Japansese – is the most pervasive, Beil said.

“All it takes is this much to spread,” Beil said, holding a ripped knotweed stem in his fingertips. “You cut it up, and each bit grows a new plant.”

A former city policy of mowing knotweed along roadsides only made things worse, said Beil.

“It got cut up – and that slows it down a little – but then you drop the mower somewhere else,” he said. “And then you have more knotweed growing farther down the road.”

Beil is employed part-time by IslandWood to eradicate invasive plants such as English ivy and Scotch broom. He also commits about 20 hours a week to combat noxious plants as a volunteer with Weed Warriors, an island invasives-busting group, and as a solo marauder.

“I just go up to people’s houses and ask if I can get rid of their Scotch broom or ivy,” he said. “One guy I asked said, ‘oh, we like how it looks and it’s not going anywhere.’ Not going anywhere! But each Scotch broom has 30,000 seeds!”

Beil said knotweed’s ability to sprout new plants from cut fragments and it’s vigorous growth put the plant at the top of his Most Wanted list.

“We have to tackle it now or we’ll be spending millions in a couple of years to take care of it,” he said.

The city’s new rules on knotweed require special training for anyone who administers the approved syringe-injection method of delivering glyphosate.

With thousands of stalks in just a few hundred feet of roadside, the new technique will be extremely labor intensive, according to city planner Marja Preston.

“The injection method is by far the most controlled method,” she said. “But it’ll take a lot of work.”

Preston is asking the council to budget about $35,000 to train staff and manage the eradication program.

She also hopes to enlist volunteers through local groups and government conservation organizations in helping to inject each stalk of knotweed.

The city heard numerous concerns in letters and emails from island residents concerned about the herbicide ban amendment.

Most comments acknowledged the dangers knotweed poses to the island environment while urging caution in the methods of applying the herbicide.

“I’m concerned about the limited use of herbicides on knotweed will quickly lead to vastly expand…herbicide application” and increased health risks in the community, wrote landscape Michael Swassing in an email to the city.

Others asked the city to limit herbicide use to knotweed and narrow down the acceptable methods for applying the chemical weed-killers.

The city listened and crafted the approved amendment with local concerns in mind, said Councilwoman Debbie Vancil.

“I was reluctant to change the (herbicide) ordinance because I was concerned that it could give unclear direction and could be diminished by some confusion,” said Vancil, who proposed four changes to the initial amendment requiring stricter herbicide use, including the rule that limits all use to the injection technique.

“Even though we work really hard to ban herbicides on Bainbridge Island, I am convinced that Japanese knotweed is a serious threat to our natural vegetation,” she said. “It’s a serious, serious issue and it’s a very aggressive plant. All the experts told us – and even many people who oppose herbicides – that glyphosate is necessary, and I believe them.”